Using Dy(dbm)3(H2O) and Dy(btfa)3(H2O)2 to react with enantiopure N-donors, (−)/(+)-4,5-pinenepyridyl-2-pyrazine (L R /L S ), respectively, two pairs of chiral DyIII enantiomers, Dy(dbm)3L R /Dy(dbm)3L S ( R-1-Dy/ S-1-Dy) and Dy(btfa)3L R /Dy(btfa)3L S ( R-2-Dy/ S-2-Dy) were obtained, wherein one of the benzene rings of dbm– (dibenzoylmethanate) in R-1-Dy/ S-1-Dy is displaced by the −CF3 group of btfa– (4,4,4-trifluoro-1-phenyl-1,3-butanedionate) in R-2-Dy/ S-2-Dy. Interestingly, this substitution results not only in giant differences in their single-ion magnetic (SIM) performances but also in their completely different nonlinear optical (NLO) responses. R-1-Dy presents a large effective energy barrier (U eff = 265.47 K) under zero applied field, being more than 4 × R-2-Dy (61.40 K). The discrepancy on their magnetic performances has been further elucidated by ab initio calculations. Meanwhile, R-1-Dy/S-1-Dy display the strongest third-harmonic generation responses (35/33 × α-SiO2) among the known lanthanide NLO-active coordination compounds (CCs). On the contrary, R-2-Dy/S-2-Dy exhibit moderate second-harmonic generation responses (0.65/0.70 × KDP). These results not only give the first example of the CCs with both SMM/SIM behavior and a THG response but also provide an efficient strategy for achieving the function regulation and switch in multifunctional CCs.
By utilizing Dy(hfac)3(H2O)2 to react with enantiomerically pure tridentate N,N,N-pincer ligands, namely (−)/(+)-2,6-bis(4′,5′-pinene-2′-pyridyl)pyridine (L R and L S ), respectively, homochiral DyIII enantiomeric pairs formulated as Dy(hfac)3L R /Dy(hfac)3L S (R -1/S -1) (hfac– = hexafluoroacetylacetonate) were achieved and structurally characterized. Meanwhile, their magnetic, photoluminescent (PL), and chiroptical properties were probed. The PL test results indicate that the precursor Dy(hfac)3(H2O)2 only shows very weak emission, while R -1 exhibits characteristic DyIII f–f transition emission bands at room temperature. Furthermore, the nonlinear optical responses of Dy(hfac)3(H2O)2, L R /L S , and R -1/S -1 were investigated in detail based on crystalline samples. The results reveal that L R and L S present the coexistence of second- and third-harmonic generation (SHG and THG) responses with more intense signals for SHG responses; and Dy(hfac)3(H2O)2 merely displays weak THG responses, while R -1 and S -1 also only exhibit THG responses. However, the THG intensities of R -1 and S -1 are more than six times larger than that of Dy(hfac)3(H2O)2 under the identical measurement conditions. These results demonstrate that introducing homochiral N,N,N-pincer ligands to replace two H2O molecules of Dy(hfac)3(H2O)2 results in significant improvements of both PL performances and THG responses of resultant R -1/S -1 enantiomers. R -1 and S -1 integrate PL, THG, and chiral optical activity in one molecule, suggesting their multifunctional merits. In particular, a convenient method is introduced to simultaneously test THG and SHG responses of molecular materials based on crystalline samples in this work.
A metal-to-metal relay recognition was discovered with sequence specificity via a fluorescence 'off-on-off' phenomenon. We present here the synthesis of a new N,N-bis(2-pyridylmethyl)amine-based fluorescent sensor termed NBPA and its application as a selective relay probe for sensing of free trace zinc and copper ions. The addition of Zn(2+) to NBPA causes a drastic enhancement of fluorescent intensity by the formation of a 1 : 1 NBPA-Zn(2+) complex whereas other cations have no response. Moreover, Cu(2+) can induce fluorescence quenching in the NBPA-Zn(2+) system by the formation of a 1 : 1 NBPA-Cu(2+) complex confirmed by Job's Plot. The signal change of the sensor is based on the chelation-enhanced fluorescence (CHEF) effect of NBPA-Zn(2+) with the inhibition of the photoinduced electron transfer (PET) effect and the paramagnetic nature of Cu(2+) to the NBPA-Zn(2+) system. Under optimized conditions, the fluorescence intensity is linear to the concentration of Zn(2+) and Cu(2+) separately, exhibiting good linearities from 1.0 × 10(-6) M to 8.0 × 10(-6) M and 1.0 × 10(-6) M to 1.0 × 10(-5) M (R(2) = 0.9996 and R(2) = 0.9914) with detection limits of 7.89 × 10(-7) M and 1.27 × 10(-7) M, respectively. Furthermore, the rapid, selective feature enables the proposed sensor to be promising in monitoring Zn(2+) and Cu(2+) in biological and environmental research with good accuracy and precision.
Lithocarpus polystachyus Rehd. is an important medicinal plant species grown in southern China, with phlorizin as its main active substance. The effects of light conditions on phlorizin biosynthesis in L. polystachyus remain unclear. Thus, we analyzed the transcriptomes of L. polystachyus plants cultivated under diverse light qualities, light intensities, and photoperiods. The light treatments resulted in 5977–8027 differentially expressed genes (DEGs), which were functionally annotated based on the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Genes encoding transcription factors from 89 families were differentially expressed after the light treatments, implying these transcription factors are photoresponsive. Phenylalanine ammonia lyase (PAL) and 4-coumarate-CoA ligase (4CL) are the key enzymes for the accumulation of phlorizin. The transcription levels of PAL2, PAL, 4CL1 (DN121614), 4CLL7, and 4CL1 (DN102161) were positively correlated with phlorizin accumulation, suggesting that these genes are important for phlorizin biosynthesis. An ultra-high-performance liquid chromatography method was used to quantify the phlorizin content. Phlorizin accumulated in response to the green light treatment and following appropriate decreases in the light intensity or appropriate increases in the duration of the light exposure. The green light, 2000 lx, and 3000 lx treatments increased the PAL activity of L. polystachyus, but the regulatory effects of the light intensity treatments on PAL activity were relatively weak. This study represents the first comprehensive analysis of the light-induced transcriptome of L. polystachyus. The study results may form the basis of future studies aimed at elucidating the molecular mechanism underlying phlorizin biosynthesis in L. polystachyus. Moreover, this study may be relevant for clarifying the regulatory effects of light on the abundance of bioactive components in medicinal plants.
The lack of highly efficient, durable, and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) working at high current densities poses a significant challenge for the large-scale implementation of hydrogen production from renewable energy. Herein, amorphous molybdenum tungsten sulfide/nitrogen-doped reduced graphene oxide nanocomposites (a-MoWS x /N-RGO) are synthesized by plasma treatment for use as high-performance HER catalysts. By adjusting the plasma treatment duration and chemical composition, an optimal a-MoWS x /N-RGO catalyst is obtained, which exhibits a low overpotential of 348 mV at a current density of 1000 mA cm −2 and almost no decay after 24 h of working at this current density, outperforming commercial platinum/carbon (Pt/C) and previously reported heteroatom-doped MoS 2 -based catalysts. Based on density functional theory (DFT) calculations, it is found that with a reasonable tungsten doping level, the catalytic active site (2S 2− ) shows excellent catalytic performance working at high current densities because extra electrons preferentially fill at 2S 2− . The introduction of tungsten tends to lower the electronic structure energy, resulting in a closer-to-zero positive 𝚫G H * . Excessive tungsten introduction, however, can lead to structural damage and a worse HER performance under high current densities. The work provides a route towards rationally designing high-performance catalysts for the HER at industrial-level currents using earth-abundant elements.
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